High harmonic generation (HHG) is a known technique for producing extreme ultraviolet radiation in rare gases. Light intensities in excess of 1013 W/cm2 are typically required. Such high intensities are not typically available directly from the driving laser so parametric amplification, which reduces the pulse repetition rate to a few kHz, is commonly used. Additional amplification stages that also operate at a pulse rate much lower than the hundreds of MHz of a mode-locked laser are commonly used as well. Furthermore, the conversion efficiency to the harmonics is extremely low, between a high of 10−5 down to 10−8 or less for the highest harmonics; in other words, the energy content of the initial laser is largely undepleted and ultimately wasted.
An example of an HHG technique is also described in U.S. Application Ser. No. 61/286,347.